Search system for radio locators



1946- M; R. BRIGGS ET AL 2,412,867

SEARCH SYSTEM FOR RADIO LOCATORS Filed Nov. 10, 1943 V 3 Sheets-Sheet l wnNsssss: V M d R gg9o l g a nar 510.444 A135! A. Mqcdonald.

A'Troim Dec. 17, 1946.

WITNESSES:

M. R. BRIGGS ET AL SEARCH SYSTEM FOR RADIO LOCATORS Filed Nov. 10, 1943 [Maynard Any z s A.

3 Sheets-Sheet 3 Eye INVENTORS R Briggs & Ma cdanald.

ATTOR Y Patented Dec. 1?, 1946 angst? UNITED STATES PATENT OFFICE 2,412,867 SEARCH SYSTEM FOR RADIO LOCATGRS Maynard R. Briggs and Angus A. Macdonald, Catonsville, Md., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 10, 1943, Serial No. 509,684

8 Claims.

Our invention relates to apparatus producing beams of electromagnetic radiation and, in particular, relates to apparatus of that type suitable for use in locating objects at a distance by means of beamsof the electromagnetic energy. Systems of this type which have recently come into wide use are known as radar'systems.

There has been a considerable development of arrangements which employ a constricted beam of ultra-short radio waves to scan distant regions in which reflecting objects, such as ships or aircraft, are expected to be present, the reflected energy of the beam being detected when the beam is in such a position as to impinge on the reflecting object. By noting the direction in which the beam' is pointed at the time reflections of energy are received; it is possible to determine the direction of the reflecting ob'jec't'. In most instances, the beam is producedbylocating a shortwave antenna close tothe focus of a parabolic reflector, and the reflector is then rotated and tilted to periodically scan the region in" which the reflecting objects are expected. In certain cases, however, the direction of the expected objects is known with a'fair degree of accuracy, and it is then possible to, maintain the reflector-pointedin the general direction and to determine the precise position of the object'by causing'a periodic displacement of the beam about the central axis of the reflector. This latter eifect may be achieved by displacing the radiating antenna, usually a small di-pole, laterally from the central axis of the refiector,and rotating it periodically about this axis in a circle; When the an tenna is displaced laterally from the focus of the reflector, the beam of radiant energy is, in effect, tilted and sent out at an angle relative to the central axis of the reflector. Thus; in Figure 1, as the double dot-and-d'ash line I represents the central axis of thereflector, the intensity of the beam with the antenna displaced laterally in the plane of the paper from the focus is represented bythe polar curve 2' shown in heavylines. It will be seen from the curve 2 that theline of greatest intensity of the beam is tilted at an angle a to the reflector-axis I. If now the an- I tenna is rotated in' a circle about the focus, the

curve 2 will rotate likewiseabout the axis I, the angle a remaining constant; v

If a beam having the configuration of that just describedstrikes a distant object which is located at a point other than on the axis I of the reflectonthe intensity of energy striking the object, and hence the intensity of the received reflection, will vary periodicallyas the antenna The highest degree of precision in determining the instant when the reflected energy is a maximum is attained when the beam sent out by the reflector is rather narrow; that is to say, when the distance t in Fig. 1 is relatively small. On the" other hand; if the antenna is maintained always so close to the focus of the reflector as to give maximum precision in the readings of the intensity of the reflected wave, the angular dis.- tance a in Fig. 1 is so small that the total solid angle swept over by the beam during one period of its rotation is relatively small; and consequently the area searched for reflecting objects is relatively limited. On this account, it is desirable that in searching for the presence of the reflecting object the antenna be displaced considerably from the focus of the reflector. Then, once the object has been picked up and its approximate direction been determined, the reflector can be turned so that its axis coincides more closely with that direction, and the antenna may then be moved closely enough to the focus of the reflector so as to give the greatest accuracy in determining the time of arrival of the maximum reflected energy.

It is, accordingly, one object of our invention to provide an arrangement in which a radiating antenna may be subjected to periodic motion relative to the focus of a reflector in such a way as to scan a relatively wide solid angle in order to pick up reflecting objects, and thereafter be moved relative to said focus in such a way as to insure a high degree of precision indetermining the direction of the reflecting object.

Another object of our invention is to provide an arrangement in which a radiating antenna may be rotated about a curve of varying radius relative to the focus of a reflector.

Another object of our invention is to provide an arrangement in which the beam of radiation sent out by a reflector energized by a source of short-wave radio may be periodically varied in effective width while at the same time it rotates periodically about the central axis of the reflector.

Still another object of our invention is to pro ported on the frame I2.

3 vide an arrangement in which an antenna may be moved about the focus of a reflector periodically in a curve of varying radius. I

Other objects of our invention will become apparent upon reading the following description,

taken in connection with the drawings, in which:

Figure 1 is an explanatory diagram representing the energy intensity plotted in polar coordinates sent out by a reflector system embodying the principles or our invention;

Fig. 2 is a view in elevation showing a reflector provided with a radiating antenna which is caused to move about the focus of the reflector, in accordance with our invention;

Fig. 3 is a sectional view through the central axis of the antenna and the concentric line supplying it, and showing details of a flexible coupling making it possible to rotate the antenna while, at the same time, displacing it at a variable radial distance from the central axis of one portion of the transmission line;

Fig. 4 is a view, partly in section and partly in elevation, of the mechanism for producing the desired movement of the antenna relative to the focus of the reflector, in accordance with our invention;

Fig. 5 is a view in elevation at right angles to the view in Fig. 4 of the same mechanism; and

Fig. 6 is a detailed view of one of the component parts of the mechanism of Figs. 4 and 5.

. Referring in detail to Figure 2, a reflector Ii which may be of any suitable conductive mate-' rial well known in the art, and which is preferably of substantially parabolic section, is mounted in a framework I2 which is suitably supported to be turned in any desired direction at will, by arrangements well known in the art, and forming no part of our present invention. The reflector I I. has a central axis I3 on which is positioned its focal point l4. Positioned with its axis concentrio with the axis I3 is a transmission line of the concentric type shown in more detail in Fig. 3. One portion I5 of the transmission line is supported in suitable bearings It on the framework 'I2, so that it may be rotated about its central axis. Such rotation may be imparted to the portion I5 by a set of bevel gears I'I transmitting motion from a suitable motor I1 which is supportion I5 passes through the interior of a chamber I8 which is attached to the reflector II, and which is shown in section in more detail in Fig. 4.

As is shown in more detail in Fig. 3, the transmission line portion I5 terminates in what may be termed an end-bell 9 having two projecting arms 2| containing set screws 22 which form gimbals in which is supported an end-bell 23 which is connected to a second concentric transmission line-portion 24. The portion 24 has a core-portion 25 concentric with its axis which terminates at the focus I4 of reflector II in an extension 26, forming one branch of the radiating antenna. The other branch 21 of the radiating antenna is attached to the line-portion 24. The line-portion 24 is likewise surrounded by an annular ring 28 of conducting material which supports a conducting sleeve 29, leaving an annular space be tween the sleeve 29 and the line-portion 24 which is approximately one-quarter wave length long. There is likewise supported on the line-portion 24, and in front of the antenna halves 26, 27, a conducting dummy-element 3 I. It may be noted The transmission line that the antenna portions 26 through 3| may be replaced by any other suitable radiating-antenna 4 arrangement adapted to the short radio. waves being utilized to produce the beam.

' The central core 32 which cooperates with the line-portion It has a slightly flared end-portion 33 having a central hole 34 concentric with its axis into which extends a cylindrical extension 35 from the core-portion 25. The width, of the annular space 34 is made sufficient so that the extension 35 will not come within sparking distance of the bell-portion 33, when the line sec: tion 24, 25 is. rotated in the gimbals 2I, 22, 23 through the maximum angle in which the ar-- rangement is intended to operate.

The line-portion I5 is provided with an extension 35 having a turned-back cuff portion 3'! which is spaced away far enough from the walls of the end-bell 23, so that it will never come within sparking distance thereof when the gimbals 2!, 22, 23 are turned through their maximum range of operation. The flared end of the endbell 23 is provided with a screw-cap 4!) which is adapted to hold in place a flexible diaphragm 38 which may, for example, be of rubber, and which has its inner edge attached to the extension 36 by a suitable collar 39 and a nut II. The length of the annular channels separating the extension 35 from the flared end 33, and separating cuff 3'! from end-bell 23, are preferably approximately one-quarter of the wave length of the radiation sent out by antenna 26, 21. Cult 3? is made electrically one-quarter wave length long by addition of an insulating material 3'1 inserted between the folded back portion 3'! and 36.

Fastened to the line-portion I5 is a gear 'wheel 42 which meshes with a second gearfwheel 43 which is supported in a bearing 44 on, frame I2. Attached to the same shaft as the gear 43 is-a third gear 45 which meshes with gear teeth on a that it can traverse the annular .path along the end-face of the member 4?. A spring 5| extending between the end-bell I9 and a stud 52 which projects from the end-bell- 23 biases the roller 49 into. contact with the, end-face of drum 41.

It will be remembered that the drum 41 rotates relative to the line-section I5 to which the endbell I9 and the gimbals 2|, 22, 23 are attached. The drum 41, accordingly, rotates relative to the end-bell 23; and as it does so, the roller 49, making contact continually under the stress of spring 5| with the end-face of drum 41, traverses an annular path on the latter the Plane of which .is not normal to the axis I3. In view of the latter reflector II; The frequency-of the, periodic mo.-

tion will, of course, be equal to the difference in number of revolutions per second of the drum 41 relative to the line-portion l5. Since the lineportion I 5 is rotating on its axis relative to the reflector II, the antenna 25, 21 will rotate relative to the reflector H at a frequency relative to the number of revolutions per second imparted by the motor H to the line-section Hi. The antenna 26, 21 will, accordingly, rotate about the focus of reflector II in a periodic curve having a radius which periodically varies between limits which are determined by the contour of the endface of the drum S1. The last-mentioned contour may, for example, lie in a plane which is other than normal to the axis l3 or, instead of being plane, this end-surface may be warped in ways obvious to those skilled in the art, to provide for the description by the antenna 26, 21 of any desired curve about the focus It.

The arrangement thus far described represents the condition in which the apparatus is intended to operate during the search period in which the approximate position of an approaching object is to be determined. By suitable oscillographic well known in the art, by which the position versus time curve representing the rotation of line-portion l5 and the intensity versus time curve for the received reflected energy can be correlated, the azimuth of the antenna 26, 21 about the axis l3 at the time when the object is closest to the center of greatest intensity in the beam from reflector H can be determined. The frame I2 can then be displaced by suitable arrangements well known in the art, but not shown here, to move the axis 13 of the reflector ll close to the direction of the object. It then becomes desirable to stop the periodic radial movement of the antenna 26, 21 relative to the focus l4, and to rotate it in a circle of relatively small diameter about that focus.

In order to eifect the result just described, we mount on the end-bell 23 a second roller 6| on a radially projecting stud. We further provide the sleeve l8 with three projecting studs 62 which support rollers 65 and extend radially inward from the sleeve l8. The rollers 65 engage a slot 66 in an annular member 61 having a projecting rim 68 provided with suitable gear teeth. A shaft 69 is supported in suitable bearings 10 on the inner face of the sleeve l8 in a position parallel to the axis l3, and is provided with a pinion 1| adapted to mesh with the gear teeth on rim 68.

The annular member 61 is formed with a ledge 13 lying in a plane normal to axis l3 and adapted to form an annular path to be traversed by roller BI. The slot 66 is so cut that the distance of its center line from the rim 6B varies with circumferential distance about the rim 68. The position of the stud 52 on the sleeve I8 is so determined that when the stud 62 engages those portions of the slot 66 which are least distant from the rim 68, the ledge 13 is displaced so far away from focus M (i. e., in Fig. 4) that it can not engage the roller Bl even when, in course of rotation of the end-bell 23 about the axis l3, the roller 49 engages the portion of the end-face of drum 41 which is most distant from focus I 4 (i. e., when it engages the portion of the end-face of drum 41 which is farthest to the left in Fig. 4). Under such circumstances, the roller 49 is able to follow in engagement of the end-face of drum 41 during the entire revolution of antenna 26, 21 about focus l4.

However, it will be observed that the member 61 stands stationary relative to the sleeve l8, framework I 2 and reflector l I, and is unmoved by the rotation of the transmission line 15-24 and all their connected parts within the framework l2, as previously described. The end of the shaft 69 is provided with suitable means, such as a motor 14, so that it may be rotated when desired. When it is desired to stop the periodic tilting of the antenna 26, 21 relative to the focus I4, after the approximate position of an approaching object has been determined, the shaft 69 is rotated; thereby imparting a rotary movement to the member 61 and causing the slot 65 to move relative to and along the stud 62. Movement of the roller 65 in the slot as will obviously move the member 61 toward focus M (i. e., move it farther to the right in Fig. 4); thereby displacing the annular ledge 13 into contact with roller 6|, and thereby preventing roller 49 from thereafter following the contour of the end-face of drum 41. Since the annular ledge 13 lies in a plane normal to the axis IS, the progress of the roller 8| about this ledge will cause no tilting of the end-bell 23 and its attached antenna 26, 21 upon the set-screws 22, but will maintain the antenna 26, 21 at a fixed radial distance from the focus M of the reflector H. The antenna 26, 21 will thereafter describe a circle of small radius about the focus Hi, this radius being determined by the number of times shaft 69 is turned, and the apparatus will be in the condition for most accurate determination of the direction of the reflecting object relative to axis l3.

Obviously, when it is desired to return the apparatus to curve of periodically varying radius about the focus M, the shaft 69 may be turned so as to move the pivot 62 to the position in slot 66 initially described.

While we have described, as required by the patent statutes, a specific mechanism for producing the desired movement of the antenna 25,.

21 relative to the focus This particular mechanism is, accordingly, only a particular embodiment of our broader invention which is the possibility inherent in providing for movement of the antenna in a periodic curve of varying radius while searching, and in following a curve of substantially constant radius about the focus while making more accurate determinations of the direction of the reflecting object We claim as our invention:

1. In a system of ultra-high frequency beam transmission, means for projecting a beam into 2. In a system of transmission, means pared with that at ried out.

3. In a system of ultra-high frequency beam transmission, means for projecting a beam into space, means for rotating said beam at a fixed angular displacement with respect to the normal axis of rotation thereof, andrmeans for gradually increasing said angular displacement at recurrent intervals'which have a periodicity small compared with that at which said rotating is carried out. I

4. In a system of ultra-high frequency beam transmission, means for projecting a beam into space, means for rotating said beam at a fixed minimum angular displacement with respect to the normal axis of rotation'thereof, and means for gradually increasing said angular displacement from said minimum position to another position of maximum displacement and gradually decreasing from said maximum displacement to said minimum displacement at recurrent intervals of fixed periodicity which is small compared with that at which said rotating is carried out.

5. In an ultra-high frequency radio locator system, means radiating a beam of ultra-high frequency energy comprising an antenna rotatably disposed near the axis of a parabolic reflector, said antenna being displaced at an angle from the axis of said parabola, means for varying the effective width of the radiated beam comprising means for changing the angle of displacement of said antenna from said angle to another angle while said antenna is being rotated.

6. In an ultra-high frequency radio locator system, means radiating a beam of ultra-high frequency energy comprising a wave guide 1'0- tatably disposed near the axis of a parabolic reflector, said wave guide being displaced at ;an angle from the axis of said parabola, means for varying the width of the radiated beamqcomprising means for changing the angle of displacement of said wave guide from said angle to another angle while said wave guide is being rotated.

'7. The method of locating an object by means of a beam of ultra-high frequency energy for the purpose of range finding which comprises, irradiating space having the form of a hollow, conical pattern, sweeping the field of search by said pattern, enlarging the effective base of said conical pattern for rough location of said object at will during sweeping said field of search, and narrowing said effective base upon location of the object for accurate determination of range.

8. The method of locating an object by means of a beam of ultra-high frequency energy for the purpose of range finding which comprises, irradiating space having the form of a hollow conical pattern sweeping the field of search by said pattern, enlarging the effective base of said conical pattern for rough location of said object at recurrent intervals of fixed periodicity during sweeping said field of search, and narrowing said effective base upon location of the object for accurate determination of range.

MAYNARD R. BRIGGS. ANGUS A. MACDONALD. 

